A buckle has been conventionally known, in which a band (or belt) is provided with an engagement groove; a hook of the buckle is elastically engaged with the groove; and such a locking state can be released at any time. In Japanese Patent No. 3982955 (Patent Document 1), the present inventors have proposed a synthetic-resin buckle that is easy to manufacture and light in weight, the buckle including: a buckle main body composed of a base plate and a roof frame opposed to each other, and two side plates connecting the base plate and the roof frame, in which an inside of the buckle main body is an insertion space for the band having an engagement groove; and an operation piece being horizontally installed inside the roof frame, and having, on an under surface of one end thereof, the engagement claw that can be engaged with the engagement groove of the band, in which an other end thereof is a pressing portion; the operation piece is connected to two sides of the opposed roof frame in an intermediate point between the engagement claw and the pressing portion, whereby allowing the operation piece to swing around the intermediate point as a fulcrum; and an outer surface of the band and the roof frame are provided with a pair of latching protrusions, with which the band can be pulled toward the buckle main body with a finger-tip of one hand.
The synthetic-resin buckle is significantly superior in function, and is optimal as a buckle for headbands of a helmet. However, if the connecting shaft is thinned to be applied to a product such as a watch band that relatively requires the buckle to be downsized, a strong force acts on the band in a direction of separating from the buckle when the band and the buckle are locked, and the synthetic-resin connecting shaft might be damaged. There was also a problem that the engagement strength of the band and the buckle deteriorates due to degradation of the elasticity over time, which is attributable to a creeping phenomenon (i.e. a property of synthetic resin to slowly deform when a strong pressure is applied to the synthetic resin for a long time).
In Japanese Patent No. 4005109 (Patent Document 2), the present inventors have also proposed a slide adjuster of a band and a buckle, which is suitably applied to products such as clothing ornaments in particular, the slide adjuster being light in weight and simple in configuration, in which the buckle portion has an inconspicuous external appearance; an engagement claw is engaged with a serrate engagement groove formed on an outer surface of a band, whereby allowing the band to approach but not to retreat relatively to the buckle in the locking state; the buckle includes: a buckle main body composed of a base plate and a roof frame opposed to each other, and two side plates connecting the base plate and the roof frame, in which an inside of the buckle main body is an insertion space for the band; and an operation plate being horizontally installed inside the roof frame, and having, on an under surface of one end thereof, the engagement claw that can be engaged with the engagement groove of the band, in which an other end thereof is a pressing portion for releasing the engagement; the operation plate is movably supported by a connecting shaft connecting the two side plates in an intermediate point between the locking claw and the pressing portion, whereby allowing the operation plate to swing around the intermediate point as a fulcrum; and an outer surface of the band and the pressing portion are provided with a pair of latching portions, with which the buckle and the band can be pulled toward each other with a finger-tip of one hand.
This slide adjuster can improve the strength of the connecting shaft by using a hard material such as metal or resin having no elasticity. However, in this case, it is necessary to provide separate parts such as a coiled spring. When such separate parts are provided, the structure of the buckle is complicated, and it has been difficult to manufacture a buckle that is light in weight, small in size, and easy to manufacture. With the synthetic-resin buckle and the slide adjuster, the buckle and the band can be pulled toward each other with a finger-tip of one hand. However, in order to withdraw the band from the buckle, it is necessary to withdraw the band with one hand, while pressing the pressing portion of the buckle with the other hand. Therefore, this was not suitable as a buckle to be used for a watch band, etc., which require the band to be withdrawn with one hand.
Patent Document 1: Japanese Patent No. 3982955
Patent Document 2: Japanese Patent No. 4005109